The present invention is directed to a viscous fluid coupling device and more particularly to a viscous fluid coupling device of the type having a separator disc in which a plurality of openings are provided which are angularly out of phase with each other and located at different radial distances relative to the center of the disc, and a valve member rotatable relative to said disc and cooperating with said openings to control the output torque produced by the couplings in at least three different stages.
Conventional viscous fluid coupling devices are used for the activation of a fan which cools an internal combustion engine of a vehicle or the like. Generally, the quantity of viscous fluid passing from the reservoir chamber to the working chamber is controlled by means of a valve member in response to the temperature of the engine in order to prevent excessive cooling of the engine and unnecessary loss of power. In conventional viscous fluid coupling devices, the valve member serves to open and close a single aperture through which the viscous fluid enters the working chamber from the reservoir chamber. Consequently, the output torque is only provided at a single level when the aperture is open to permit the entry of the viscous fluid into the working chamber. U.S. Pat. No. 3,463,282 shows such a viscous fluid coupling device where a single supply aperture is under control of a valve member. Such conventional viscous fluid coupling devices suffer from the disadvantage that the transmission of output torque is either very small or very large so that the cooling effect is either insufficient or excessive. When the transmission of torque is greater than necessary, there is an undesirable increase in the noise level with an attendant power loss.